RFR: 6788481: CellEditorListener.editingCanceled is never called

[Prasanta Sadhukhan]

When editing of a table cell is canceled, the function editingCanceled of the registered listener CellEditorListener is not called as actionPerformed on ESC key press was not notifying the "cancel" listeners.
Fix is to handle "Cancel" action in actionPerformed() by forwarding the Cancel message from CellEditor to the delegate so that it can call `AbstractCellEditor.fireEditingCanceled(`) which notifies all listeners of cancel event.

-------------

Commit messages:
 - 6788481: CellEditorListener.editingCanceled is never called

Changes: https://git.openjdk.org/jdk/pull/10964/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10964&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-6788481
  Stats: 114 lines in 2 files changed: 114 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10964.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10964/head:pull/10964

PR: https://git.openjdk.org/jdk/pull/10964